1. Field of the Invention
The present invention relates to a liquid container, e.g., a liquid container that utilizes a negative pressure to supply a liquid such as ink from the inside of the liquid container to a pen or an inkjet recording head as a recording section. The invention also relates to an inkjet cartridge provided by integrating a liquid container as an ink tank and an inkjet recording head.
2. Description of the Related Art
Known containers for containing a liquid include containers that supply a liquid to the outside with a negative pressure maintained inside the containers. A container of this type is characterized in that a liquid can be properly supplied to a liquid-consuming section such as a pen point or recording head connected to the container utilizing a negative pressure applied by the container itself.
The method of supplying a liquid while maintaining a constant negative pressure relative to the outside is well known in the field of inkjet printing. For example, an ink tank can properly supply ink for an ink ejecting operation of a recording head that ejects the supplied ink by maintaining a negative pressure within a predetermined range relative to a pressure in the recording head, and the negative pressure also prevents the leakage of ink from the ink tank itself when the ink tank is treated alone.
An ink supply system extending from a liquid container or ink tank to a recording head is an enclosed system utilizing a tube. In general, in the field of inkjet printing utilizing enclosed ink supply systems, the systems are categorized into systems having a mechanism for generating a negative pressure in a positive way and systems having no such mechanism. Known ink supply systems that utilize no negative pressure generating mechanism include those which utilize “a head difference” (a pressure difference generated by a difference in height between an ink supply system and an ink-consuming section). In this case, since there is no special requirement for such ink tanks except that they must be provided in a position lower than a recording head, they often have configurations like normal bags. However, since the ink supply channel is an enclosed type, there is a need for a supply line such as a tube extending from an ink containing bag to an ink-consuming section (head section) located above the same, which results in a large device. Further, limits are put on the layout of constituent parts to achieve a required head difference.
Under such circumstances, in order to make such an ink supply channel as small as possible or to eliminate the same substantially, structures of recording heads and ink tanks have been proposed and implemented in which a mechanism for generating a pressure that is negative relative to the pressure in a recording head is provided to eliminate a need for a head difference. In this specification, a unit formed by integrating an inkjet recording head and an ink tank is referred to as “inkjet cartridge” or “print head unit”.
Such inkjet cartridges having a negative pressure generating mechanism can be categorized into configurations in which a recording head and an ink containing section is always integral with each other and configurations in which a recording head and an ink containing section are separate from each other, are both separable from an apparatus main body, and are integrated with each other for use. In any configuration, an ink supply port of an ink containing section is often provided below the center of the ink containing section in order to improve the utilization of ink contained in the ink containing section. It is necessary also in this respect to supply ink properly by, for example, preventing the leakage of ink from an ejecting section such as a nozzle provided at a recording head and to provide a negative pressure for stably keeping ink in an ink containing section of an inkjet cartridge. The term “negative pressure” means a back pressure associated with the supply of ink to a recording head that is so called because it is generated for making a pressure at an ejection port section of the recording head negative to the atmospheric pressure.
In one specific configuration for generating a negative pressure, a porous member is used to generate a negative pressure by utilizing a capillary force of the same. Specifically, a porous member such as a sponge is contained in an ink tank preferably in a compressed state, and an atmosphere communication port for establishing communication between the interior of the tank and the atmosphere is provided in a position away from an ink supply port.
Negative pressure characteristics of such an ink tank in which a negative pressure is generated utilizing a capillary force of a porous member can be set in adequate ranges by adjusting the capillary force of the porous member itself, which allows ink to be supplied to a recording head with stability.
The ink containing efficiency of such an ink tank utilizing a porous member is basically low because of the presence of the porous member. On the contrary, structures are known in which a porous member is provided such that it occupies only a part of the interior of an ink tank instead of entirely occupying the interior. In this case, the porous member is contained in a part of the ink tank where an ink supply port is provided, and ink is directly contained in a part away from the ink supply port.
This structure makes it possible to achieve higher ink containing efficiency and ink holding capability per unit volume when compared to configurations in which a porous body is inserted such that it occupies an ink tank entirely.
However, the use of a porous member is still unsatisfactory when a further improvement of ink containing efficiency is considered.
On the contrary, bag-shaped containers formed by combining a bag and a spring and ink tanks utilizing an ink container made of rubber are known, and they are regarded as having relatively high containing efficiency because ink is directly contained. For example, known configurations include configurations in which a spring is provided in a bag-shaped ink containing section to provide a force acting against inward deformation of the back as a result of ink extraction, thereby generating a negative pressure (see Japanese Patent Application Laid-open No. 56-67269 (1981) and Japanese Patent Application Laid-open No. 6-226993 (1994)) and configurations in which a conical tip portion of an ink containing section made of rubber having a conical shape is rounded and made thinner than the thickness of a conical circumferential section as disclosed in U.S. Pat. No. 4,509,062.
An ink tank in which a spring is used in a bag-shaped ink container to generate a negative pressure is advantageous in that negative pressure designing can be more easily achieved than using a porous member because a reaction force of the spring in contact with a sheet of the bag is used by converting it into a negative pressure and because the negative pressure can be adjusted by designing the spring appropriately.
However, such an ink tank in the related art utilizing a spring and a sheet may have a problem associated with negative pressure characteristics of the same in that the range in which ink can be supplied with a stable negative pressure is small or in that the behavior of the negative pressure is unstable.
Ink tanks in the related art utilizing a spring and a sheet include ink tanks having a relatively large capacity (in the range from 30 to 40 cc, for example). The shape of the sheet material of such a tank is likely to vary for reasons associated with manufacture, and this results in high possibility of variations of the shape of the sheet material when ink is extracted. Consequently, the negative pressure may be out of a certain preferable range when ink is extracted in many regions, and negative pressure characteristics during ink extraction may vary from tank to tank or between ink supplying actions. This may result not only in unstable ink supply but also in an increase in the amount of extracted ink in regions where an initial negative pressure is not in the preferable range, for example.
An ink tank having a relatively large capacity is practicable in spite of the fact that it still has variations and unstableness as described above because the force of the spring to generate a negative pressure is great and the rigidity of the sheet that changes according to the amount of ink is therefore relatively small.
However, the above-mentioned problem becomes more significant when such a configuration in the related art is used for an ink container having a relatively small capacity (e.g., a capacity up to 30 cc). In particular, since the amount of ink that is used under a negative pressure in an unpreferred range increases, it may not be possible to extract a sufficient amount of ink in a preferable state of supply.
That is, when an ink container having a relatively small capacity is used, since a spring force for generating a required negative pressure is small, there is a relative increase in the influence of the rigidity of the sheet of the container on the spring force during negative pressure designing, which results in a need for paying attention to both of the spring force and rigidity of the sheet.
When such an ink container having a small capacity (e.g., a capacity up to 30 cc) is manufactured from a sheet by inflating a planar sheet and bonding or welding the same to a frame while maintaining the inflated shape, stability of assembly and reliability of bonding may be reduced because of wrinkles formed on the bonded or welded surface. Such a method of manufacture may result in a reduction of yield or variation of the ink capacity itself.
In the case of an ink tank in which no spring is provided and in which a negative pressure is generated by changing the thickness of the sheet to control the rigidity of the sheet, a problem arises in that the deformation of the sheet as a result of ink consumption likely to vary and in that the variation of the negative pressure becomes more significant when changes in the sheet rigidity according to the ambient temperature are taken into consideration.
When a liquid container as described above is stored or left unused for a long time, since a negative pressure exists in the ink tank, gases such as oxygen and nitrogen pass through the sheet and frame member to enter the ink tank. In such a case, in the case of an open type or semi-enclosed type liquid container, there is no need for considering an effect of increasing the internal pressure of the liquid container that is attributable to storage for a long time or changes in the atmospheric pressure because a part of the container is in communication with the atmosphere. In the case of an enclosed type liquid container, however, ink meniscuses can be broken to lead to leakage of ink from the ink ejection port when the internal pressure of the container increases to reach or exceed a meniscus holding pressure at the ejection port as a result of inflow of gasses.
In particular, except for soft films used in the related art taking gas blocking properties into consideration, the gas blocking properties of materials used for a rigid structural member forming an ink container or recording head may not be so good because they are selected for less influence on ink and capability of being bonded to a sheet. In this case, there is considered a remarkable relation between permeation of gases through the rigid structural member and an increase in the internal pressure of the liquid container.
When a sponge as a negative pressure generation source is contained in a liquid container, gasses that enter cells of the sponge as a result of a reduction in the amount of ink therein serve as a material for buffering an increase of the internal pressure. However, in the case of a liquid container constituted by a spring and a resin sheet, gasses will significantly contribute to an increase of the internal pressure of the container when attention is paid to the fact that only a liquid exists in the same and that the interior is in a sealed state.
In addition, there is a need for suppressing evaporation of moisture that passes through a member used for a liquid container in order to prevent any increase in the density of a liquid in the container.
Referring to configurations of such springs, coil springs and leaf springs are primarily used. In the case of a coil spring, sections of the coil pile up on one another in a compressed state when a moving section is deformed and closed as ink is consumed, which results in a thickness equivalent to the coil diameter multiplied by the number of turns of the same. This increases a dead space in an ink tank and adversely affects ink utilization. Japanese Patent Application Laid-open No. 2000-103078 has proposed a configuration in which a leaf spring having a plurality of bent sections. When a plurality of bent sections and a leaf spring are used, there will be a great spring load, which is unpreferred in that a negative pressure that is greater than an adequate value is generated especially when an ink tank is configured compactly.
On the contrary, a semi-elliptic spring has been proposed in Japanese Patent Application Laid-open No. 6-226993 (1994). According to the publication, the shape of the semi-elliptic spring is not complicated, and the spring load can be set with a certain degree of freedom according to parameters such as the thickness and material of the spring.
It is uncertain whether the semi-elliptic spring disclosed in the above-cited publication has a plate-like configuration or a linear configuration. In either case, a spring that is a single member is bent near the center thereof to generate a spring force through such bending. When a deforming load is repeatedly applied to the spring, fatigue occurs at the bent portion, which can finally result in breakage. Further, the spring must have a certain radius of curvature to be bent, which results in a dead space that is equivalent to the radius of curvature when the spring is completely compressed just as in the case of the use of a coil spring.
Specifically, a semi-elliptic spring is not suitable for an ink tank having a configuration in which ink is repeatedly charged and used, and it also has problems to be solved with respect to ink utilization. While the same publication has disclosed a configuration in which movable parts are formed symmetrically on both sides of a semi-elliptic spring, a force to deform the movable parts can act off balance because of the presence of a bent portion, which can result in unstable deformation of the movable parts or can cause variations of deformation of the movable part on one side to adversely affect the movable part on the other side through the semi-elliptic spring. Resultant fluctuations of the pressure in the ink tank can act on the printing head through the ink supply channel to adversely affect the ejecting performance.
Inkjet printing apparatus for forming an image on a printing medium by applying ink to the printing medium using an inkjet printing head include apparatus which forms an image by ejecting ink while moving a printing head relative to a printing medium and apparatus which forms an image by ejecting ink while moving a printing medium relative to a fixed printing head.
The significant recent trend toward color recording techniques has resulted in the advent of inkjet recording apparatus that have a plurality of ink tanks in order to render a plurality of colors. In inkjet recording apparatus according to the related art having a plurality of ink tanks, configurations are employed in which a plurality of ink tanks are held by an integral holding member and in which partition walls for preventing interference between the ink tanks are disposed in the holding member to allow each of the ink tanks to have an independent and stable ink containing volume and ink supplying performance, thereby keeping each of the ink tanks in an independent state. Alternatively, a holding member itself may be independently configured for each color and independently and detachably fixed to a fixing member at a recording apparatus main body.
However, a configuration in which a plurality of ink tanks are provided for color recording results in an increase in the size of an apparatus in contradiction to needs for more compact recording apparatus. Although efforts have been made to provide a plurality of ink tanks close to each other for this reason, it is rather difficult to provide a plurality of ink tanks close to each other because of mechanical restrictions placed by an ink supply connecting section on a printing head main body for ejecting ink in each color. When an ink tank or container for each color can be replaced independently, since restrictions are placed on the position of an ink supply connecting section in order to supply ink to a printing head main body with reliability, ink tanks have been kept separate from each other by partitions with some degree of freedom to prevent interference between them in order to give priority to the reliability of ink supply.
The above-described arrangements create a problem especially when a configuration is adopted in which ink is supplied by attaching ink tanks integrally with or detachably from a printing head that is mounted on a carriage to be moved back and forth (main scanning). Specifically, when members moving with a carriage (a printing head and ink tanks undetachably or detachably integrated with the same) have a large projected area in the direction of a plane perpendicular to the direction of main scanning or a large volume, a grate space will be required for main scanning, which will result in an increase in the size of the apparatus as a whole.